The contact pathway of the plasma clotting cascade is dispensable for normal hemostasis, but contributes to
thrombosis and serves as a bridge between
inflammation and coagulation. This pathway is triggered upon exposure of plasma to certain anionic
polymers and artificial surfaces. Recently, extracellular
nucleic acids and inorganic
polyphosphate (
polyP) have been implicated as being important (patho)physiologically relevant activators of this pathway. However, mechanistic details regarding how
nucleic acids or
polyP modulate the individual reactions of the contact pathway have been lacking. In this study, we investigate the ability of
RNA homopolymers and
polyP to bind the primary constituents of the contact pathway:
factor XIa,
factor XIIa, and
plasma kallikrein, in the presence and absence of
high molecular weight kininogen (HK), an important cofactor in this pathway. We examine seven proteolytic activation reactions within the contact pathway and report that
polyP greatly enhances the rate of all seven, while
RNA is effective in supporting only a subset of these reactions. HK both enhances and suppresses these proteolytic activation reactions, depending on the specific reaction evaluated. Overall, we find that
polyP is a potent mediator of contact pathway activation reactions in general, that
RNA secondary structure may be important to its procoagulant activity, and that
nucleic acids versus
polyP may differentially modulate specific enzyme activation events within the contact pathway.